Diverse devices have been employed for positioning a workpiece in a predetermined angular position with respect to a rotatable head stock and/or tail stock, prior to locking the opposite ends of the workpiece within the head stock and tail stock. When grinding a cam shaft, it is necessary to establish the workpiece in a fixed angular position with respect to locating means on the cam shaft, and to maintain such angular relationship, so that the lobes on the finished product are in proper angular relation with one another.
U.S. Pat. No. 3,667,167, granted to Happel, discloses a device for maintaining a workpiece in a fixed angular relation with respect to a master cam shaft so that the lobes on the finished product are in proper angular relation with one another. The master cam and drive spindle rotate in synchronism. The device includes a pair of opposing lock surfaces which engage a key that extends from a slot in the workpiece. Both of the lock surfaces are pivotably mounted to a backing plate, and springs actuate the plate to engage the key.
U.S. Pat. No. 2,984,955, granted May 1961, to Price, discloses another device for positively locating a workpiece with respect to a rotatable drive spindle. In this device, the drive spindle extends outward from a drive plate to engage a conical recess located in the end of a longitudinally extending workpiece. The workpiece is rotated about its axis by the drive spindle, and a pin is mounted in the drive plate at a location radially spaced from the spindle. The pin may be moved axially to engage a second recess in the workpiece in order to locate the workpiece in a predetermined angular relation with respect to the spindle and drive plate.
U.S. Pat. No. 4,207,710, granted Jun. 17, 1980, to Roger H. Fournier, discloses a workpiece positioning system (12) which holds a workpiece (14) in a predetermined angular position relative to a rotating drive spindle (20) of a machine, such as a cam shaft grinder or a pinion gear grinder. The workpiece is provided with a keyway (40) and a key (42; as shown in FIG. 2). The apparatus includes a drive element (sleeve 80) having a drive surface (73) which is rotated into engagement with one side of the key on the workpiece. Further rotation of the drive element rotates the workpiece and brings the opposite side of the key into engagement with an index surface (74--FIG. 5) on the positioning apparatus. Holding the key against the index surface maintains the workpiece in a predetermined angular relationship with the drive spindle during a grinding operation. The workpiece positioning apparatus includes a fluid actuated motor (75; see FIGS. 6 and 7), which rotates with the spindle and is operable to rotate the drive element.
A more sophisticated workpiece orienting system is disclosed in U.S. Pat. No. 3,863,402, granted Feb. 4, 1975, to Ralph E. Price. A loader is incorporated into such system, which is thus better suited for high speed processing of workpieces, for such system does not rely upon keys and slots, pins and recesses, etc. and other complementary mechanical alignment devices to properly orient the workpiece relative to the drive spindle.
Price discloses a workpiece orienting device, such as station 20, comprising a chute 10 for supporting a randomly oriented workpiece W, having an eccentric portion (cam lobe 40) to be ground to size. The workpiece is engaged by, and supported by, work centers 26, 28, which are axially advanced into engagement with the workpiece by hydraulic cylinders 36, 38. Hydraulic motor 32 slowly drives the workpiece W. An orienting finger 42 is selectively located to be radially aligned with the eccentric portion of the supported workpiece. The orienting finger is normally retained in a retracted position, as shown in solid outline in FIG. 3, but is advanced into engagement with the cam lobe 40 after a predetermined interval controlled by operating lever 48, limit switch 50, etc. The bearing surface 44 of finger 42 contacts the periphery of the cam lobe with sufficient force to prevent further rotation of the workpiece, as noted in column 2, lines 35-41. The workpiece is thus arrested at a predetermined angular position, prior to grinding, under the control of a master cam--note column 2, lines 17-23.
The foregoing patents disclose complex systems that angularly orient workpieces, in a machine tool, in a particular manner, before clamping same in a fixed position, and then initiating machining operations. The systems rely upon two speed motors, in some instances, and cooperating mechanisms, to sense the eccentric surfaces on a workpiece rotated at slow speeds. Then, after clamping the workpiece in fixed position between the spindles of the head stock and tail stock, machining operations take place under the control of the second, high speed motor.
Such systems function satisfactorily, when the workpiece has similar cylindrical ends. However, such systems are seemingly incapable of orienting workpieces which are characterized by an axially projecting pin at one end thereof.
Furthermore, the speed of operation of known orienting systems is inadequate to meet the demands of current high speed production lines, and such limitations have created a demand for a simple, effective, and rapid system for orienting a chucking mechanism, with a locator retained therein, relative to a workpiece with a protruding pin. The present invention seeks to overcome the shortcomings of known workpiece orienting systems, by focusing upon angularly orienting a locator in the chucking mechanism relative to the pin on the workpiece. The present invention relies upon a proximity sensor in an otherwise conventional loader, to "read" the eccentric surfaces on the workpiece, and adjust the position of the chuck in reliance upon such "reading".